From AMS Glossary
Analytical technique in which an atom or molecule absorbs and then emits radiation of a specific frequency, followed by detection of the emitted radiation.
The radiation is usually provided by a plasma containing the atom or molecule to be detected, ensuring that radiation of the correct frequency is available (hence the term resonance). The technique has been adapted with great success to atmospheric measurements, for example, the measurement of ClO radicals in the antarctic ozone hole.
Anderson, J. G., D. W. Toohey, and W. H. Brune 1991. Free radicals within the Antarctic vortex: The role of CFCs in Antarctic ozone loss. Science. 251. p. 39.